The present invention relates to phenol-functional resins cured with isocyanate cross-linking agents and more particularly to such a system which is curable in the presence of a vaporous tertiary-amine catalyst.
Vapor Permeation Cure (VPC) has been proposed on a limited basis by the prior art. For example, U.S. Pat. No. 2,967,117 shows a coating composed of a polyhydroxy polyester and a polyisocyanate which are cured in the presence of a gaseous tertiary amine or phosphine. The polyester contains aliphatic hydroxyl groups and heating of the coated substrate at about 60.degree.-120.degree. C. prior to or concomitant with the vaporous tertiary amine exposure is taught in the specification and examples. U.S. Pat. No. 3,874,898 shows a coating composed of a polymer containing only isocyanate functionality which can be cured in the presence of a vaporous amine. VPC technology additionally has been used for curing foundry binder compositions of a phenol-aldehyde resin (U.S. Pat. No. 3,409,579). Relative to the benzylic ether phenolic resin disclosed therein, reference also is made to U.S. Pat. Nos. 3,485,797, 3,676,392, and 3,501,552. For coatings applications, a hydroxy functional polyester may be end-capped with hydroxybenzoic acid as taught in U.S. Pat. No. 3,836,491, a phenol reacted with an unsaturated fatty acid or the like as taught in U.S. Pat. No. 3,822,226, or an epoxy polymer capped with hydroxybenzoic acid as taught in U.S. Pat. No. 3,789,044. British Pat. No. 1,351,881 modifies a polyhydroxy, polyepoxy, or polycarboxyl resin with the reaction product of a phenol and an aldehyde. The reaction product is curable with an isocyanate cross-linking agent in the presence of a vaporous tertiary amine. British Pat. No. 1,369,351 proposes a hydroxy or epoxy compound which has been reacted with diphenolic acid. The resulting compound is curable with a polyisocyanate according to VPC techniques.
In the coating compositions proposed by the foregoing art, the phenol-functionality is provided by the reaction of carboxyl functionality contained with the phenol group, e.g. hydroxybenzoic acid, diphenolic acid, and the like. The present invention, however, is directed to synthesis of compounds containing phenol-functionality for VPC coatings where hydroxyl functionality contained with the phenol group is utilized in the synthesis schemes. While such synthesis would appear to be capable of easy reduction to practice, several unexpected impediments in the synthesis schemes was uncovered during research to develop the present invention as will be more fully set forth herein.